Orthodontics has become a popular dental treatment where an orthodontic archwire is one of the main materials used in this treatment. At present, common orthodontic archwires used include stainless steel wires or β-Ti and Ni—Ti shape memory alloy wires. Andreasen uses a Ni—Ti alloy in orthodontic archwires [G. F. Andreasen, U.S. Pat. No. 4,037,324, (1977)], Burstone et al. are pioneers in using β-Ti material [C. J. Burstone and A. J. Goldberg, U.S. Pat. No. 4,197,643, (1980)]. Other ingredients are also introduced to form orthodontic archwires of various compositions [R. C. L. Sachdeva and F. Farzin, U.S. Pat. No. 5,683,245, (1997); K. Mitose and T. Ueki, U.S. Pat. No. 5,951,793, (1999); L. C. Schetky, M. H. Wu, C.-Y. Loi, and C. J. Burstone, U.S. Pat. No. 6,258,182, (2001); J. A. Davidson, A. K. Mishra, K. P. Daigle, and P. Kovacs, U.S. Pat. No. 5,573,401, (1996)]. Dental crowns are also commonly used for dental care. Metallic dental crowns are made either with noble metals or base metals, such as NiCr alloys.
The above-mentioned orthodontic archwires and metallic crowns all have bright metallic color. For cosmetic reasons, some orthodontic archwires are transparent, or even transparent with a nano structure. For example, Lemchen recently proposed a very different mesoporous alloidal orthodontic archwire [M. S. Lemchen, U.S. Pat. No. 6,056,545, (2000)]. The mesoporous alloidal orthodontic archwire invented by Lemchen has a transparency derived from the mesoporous nature thereof; it is expected that the mechanical strength thereof is inferior to the original dense material. This is a serious restriction on the use of orthodontic archwires.
U.S. Pat. No. 3,422,535 discloses a dental crown, which is anodized to provide an aesthetically pleasing color, such as gold.
US 2004/0117001 discloses anodizing archwires, among other medial implants, in order to provide a highly biocompatible surface, which resists corrosion.
US 2003/0059737 discloses a titanium oral device, which may be anodized in order to change its color.
U.S. Pat. No. 3,616,279 discloses a method for anodizing titanium and titanium alloys to provide a corrosion-resisting coating, which may vary in color depending on the applied voltage.
Japanese patent publication No. 02-115362 discloses a Ni—Ti shape memory alloy showing gold color, wherein nitrogen is ionized, accelerated and implanted into the surface of the Ni—Ti alloy, and the nitrogen-implanted Ni—Ti alloy is then heat-treated in vacuum or in an inert gas to form a compound layer of TiN showing an attractive gold color on the surface of the Ni—Ti alloy. The Ni—Ti alloy having gold color can be used as an orthodontic archwire.
Among the techniques available currently, there is no disclosure of a metallic orthodontic archwire having more than one colors on the surface thereof, and in particular by an anodizing treatment.